Stabilized mineral oil composition



Patented Apr. 2 8, 1942 STABILIZED MINERAL OIL COMPOSITION Everett W. Fuller, Woodbury, N. J., assignor to Socony-Vacuum Oil Company, Incorporated,

New York, N. Y., a corporation of New York No Drawing. Application February 18, 1939, Serial No. 257,097

5 Claims.

This invention is concerned with the stabilization of viscous mineral oil fractions against the harmful effects of oxidation or deterioration with use by the addition of an oxidation inhibitor or antioxidant to the oil. The invention is more specifically related to the improvement or stabilization of such mineral oil fractions by the use of novel compounds, or a novel class of compounds, which when admixed with a viscous mineral oil in minor proportions will prevent or delay undesirable changes taking place in the oil.

As is well known to those familiar with the art, substantially all the various fractions obtained from mineral oils and refined for their various uses are susceptibie to oxidation. The susceptibility of an oil fraction to oxidation and the manner in which oxidation manifests itself within the oil varies with the type and degree of refinement to which the oil has been subjected and with the conditions under which it is used or tested. In other words, the products formed in an oil fraction as a result of oxidation and the degree to which they are formed depends upon the extent to which the various unstable constituents or constituents which may act as oxidation catalysts have been removed by refinin operations, and also upon the conditions of use.

A highly refined" viscous oil, for example,

which is normally one that hasbeen refined by If treatment with fuming sulfuric acid or other means or combinations such as'AlCla, solvents and acids (or with large quantities of concentrated sulfuric acid), tends to form relatively large amounts of acidic constituents when subjeoted to oxidizing conditions. The presence of catalytic materials such as copper does not appear to afiect appreciably the oxidation of highly refined oils and such oils are less prone to the formation of colored bodies or of insoluble sludge. The formation of acidic bodies, however, is highly undesirable for most applications of these oils. For example, when used as an insulating or cooling oil in electrical equipment such as transformers or capacitors an increase in acidic bodies tends to lower the dielectric strength of the oil and has other harmful effects which are undesirable. The acids are corrosive to metals and thus reduce the useful life of the oils as lubricants or for other purposes in which they come in contact with metals, and the acidic materials are also injurious in textile lubricants and in spray oils.

Moderately refined oils, that is, oils that have been refined by treatment with only moderate amounts of sulfuric acid, or other refining agents,

' tend to form relatively small amounts of acidic oxidation products as compared with highly refined oils, but they undergo material color depreciation and form considerable amounts of sludge. The changes taking place in these oils are appreciably accelerated'by' the presence of metal catalysts such as copper. Suflicient acid is generally formed to cause some reduction in thedielectric strength of these oils, but the prinv cipal objection to them is their tendency to de posit sludge which interferes with heat transfer in transformers and turbines and also causes plugging of oil feed lines in lubricating systems.

Solvent-refined oils such as have been prepared by treatment with selective solvents such as Chlorex, furfural, phenol, etc., in general re semble the moderately refined acid-treated oils in that their oxidation is accelerated by the presence of metals such as copper and further in that it is attended by substantial color depreciation and sludge formation. Acid formation is usually greater than in the case of moderately acid-refined oils, but considerably less than with highly refinedoils. Both sludge and acid formation lower their value for many purposes, such as electrical insulation, lubrication,-etc. Also, solvent-refined oils have found extensive use as lubricants for internal combustion engines because of their high viscosity index, but under the conditions of use encountered in crankcases such oils develop constituents which are corrosive toward certain metals such as are typified by cadmium-silver bearings, etc., which are sometimes used. I

It is to be understood that this classification of oils as highly refined, moderately refined and solvent-refined is by no means limiting and that there can exist oils whose refining and I blending has been such as to make them interample, require much less refining to produce highly refined oils than the Coastal type of oil.

The use of oxidation inhibitors for the purpose of stabilizing a. viscous mineral oil fraction against the deleterious effects of oxidation discussed above is well known. Since the action of these inhibiting materials is apparently catalytic, the problem of their development is a difiicult one and is evidently influenced to a large degree by the oxidizable constituents which are in the oil following a particular refining treatment. Thus, a particular inhibitor or class of inhibitors may be effective to stabilize a highly refined oil against acid formation while the same inhibitor may have no appreciable effect upon acid, color or sludge formation in a moderately refined oiland vice versa. This same inhibitor may or may not be effective in inhibiting acid, sludge and color formation in a solvent-refined oil and may or may not be effective to inhibit the corrosive action of a solvent-refined oil toward metals such as used in cadmium-silver bearings. Also, the action of a compound or class of compounds upon the oxidation of light distillates such as gasoline, kerosene and the like gives no indication as to the efiect which the same compound or class of compounds will have upon oxidation of. a viscous mineral oil fraction.

The present invention contemplates improved viscous mineral oil compositions formed from all three of the typical base stocks described above. However, it appears that the compounds contemplated herein as antioxidants are of minor effectiveness in moderately refined oils, and for this reason preference is given to highly refined oils and solvent-refined oils as the types of base stocks which respond most readily to the antioxidants contemplated herein.

My invention is predicated upon the discovery that certain paranitroso dialkyl anilines are effective to inhibit the deleterious efiects of oxidation in viscous mineral oil compositions and contemplates this general class of compounds as antioxidants for such oils.

The para-nitroso dialkyl anilines are compounds having the general formula above has been demonstrated by typical oxida tion tests designed to bring out the characteristic properties of the different oils. A brief description of these tests together with the results obtained will be discussed in the following exam- This test involved heating a 150 gram sample of the oil (or the oil blend) to a temperature of 120 C. and bubbling oxygen gas through the oil for 70 hours The amount of acidic oxidation product formed during the test was determined by (a) extracting the oil with alcoholic soda, neutralizing the extract and weighing the precipitated material, which is reported as acidic sludge and (b) by titrating a sample of the oil with alcoholic potash and expressing the results as neutralization number (N. N.) which represents the amount of KOH in milligrams necessary to neutralize one gram of oil.

The oil used in the test was a highly refined oil suitable for use in transformers and the like which had been obtained from a Coastal distillate by successive treatments with 40 lbs. per bbl. of 98 per cent sulfuric acid and 180 lbs. per bbl. of 103 per cent oleum, followed by neutralization, washing and clay percolation. This oil had a specific gravity of 0.871, a hash point of 310 F., a Saybolt viscosity of 69 seconds at F. and a Lovibond color of less than 0.1.

In Table I below results are given for two representative compounds belonging to the general class contemplated herein. In this table oils A and A1 represent the oil alone; oil B is the same oil saturated 0.10%) with paranitroso dimethyl aniline; and oil C is the oil saturated 0.10%) with paranitroso diethyl aniline.

Table I Acidic products formed 15% acidic tar. 0.01% acid ter. 25 N N EXAMPLE B v (MooEBATELY REFINED OIL) The oil used in this test was a base stock of the light turbine oil type obtained from a blend of 92 per cent Mid-Continent distillate and 8 per cent Coastal distillate by treatment with 70 lbs.

per bbl. of 98 per cent sulfuric acid followed by.

neutralization, washing, and clay percolation. It had a. specific gravity of 0.879, a flash point of 385 F. and a Saybolt viscosity of 152 seconds at 100 F. This oil when subjected to elevated temperature tends to deteriorate in color and to form acidic constituents. The test used, known as the Brown-Boveri turbine oil test, in-

volved heating a test sample of the oil in the,

presence of a piece of copper foil at a temperature of C. in air for 72 hours, after which the color and neutralization number (N. N.) are determined as indicative of theextent to which the oil is afiected by oxidation. The results are given in Table II below, where oil A is the oil alone; oil B is the same oil saturated 0.1il%) with paranitroso dimethyl aniline; and oil (2" paranitrosodialkyl anilines to be of minor effectiveness in inhibiting the oxidation of moderately refined oils.

I ELE. o

(SOLVENT-REFINED One) A solvent-refined motor oil was tested for alloy bearing corrosivenss by placing within a 30 gram sample of the oil (orv oil blend) a section of a bearing containing-a cadmium-silver alloy; heating the oil to a temperature of for a period of 22 hours during which time a stream of air was bubbled against the surface of the bearing. The loss in weight of the bearing section during the treatment is a measure of the amount of corrosion taking place. The oil sample used in this t t was obtained from a Fennsvlvania mixed 'the tests on all three runs were conducted simultaneously. Oil A represents the oil alone and oils B and (2" represent the same oil saturated 0.25%-) with paranitroso dimethyl aniline and paranitroso diethyl aniline, respectively.

Table III Milligram loss in weight Oil In addition to the foregoing test on oil stocks of the solvent-refined motor oil type, a solventrefined turbine oil stock was subjected to the Brown-Boveri turbine oil test described above under Example B. The oil sample used in this test was a blend of 92 per cent Mid-Continent distillate and 8 per cent Coastal distillate which had been refined by eight-stage extraction with furfural to a rafiinate yield of '75 per cent, followed by clay percolation. The oil had a specific gravity of 0.866, a flash point of 375 F. and a Saybolt viscosity of 136 seconds at 100 F.

The results of this series of tests are listed in Table IV below, where oil A is the solvent-refined turbine oil alone and oils "3 and "C" are the same 011 stock blended with .10 per cent paranitroso dimethyl aniline and paranitroso diethyl aniline respectively.

Table IV Lovibond Oil color N. N;

A 50 0.18 B s 0.02 n 9 0.02

It will be seen from the foregoing results that the'compounds contemplated herein are effective in very small amounts to effect substantial inhibition of the deleterious efiects of oxidation upon solvent-refined oils. 4

The representative compounds tested to demonstrate the effectiveness of the antioxidants contemplated herein are only slightly soluble in viscous mineral oil fractions and may be used in varying amounts from 0.01 per cent to satu- 3 ration depending upon the oil traction and the conditions of use. Also, if desired, their solu-- tion may be facilitated by the use of a suitable solvent such as benzol.

' It is to be understood that ,the terms highly refined, moderately refined and solvent-refined as used herein are not necessarily confined to viscous oil fractions which have been subjected to a particular refining treatment but are intended as inclusive of all viscous mineral oil fractions which are similar to the foregoing examples illustrative of these types in their oxidation characteristics and inhibitor response. As has been previously pointed out, these characteristics of a viscous mineral oil fraction are governed by the crude stock from which the oil is obtained as well as by the refining treatment, and it is possible, for example, to obtain a highly refined oil from a selected crude stock by arefining treatment which would yield a moderately refined" oil from another crude stock.

I claim:

1. A viscous mineral oil fraction of the lubricant type having in admixture therewith a minor proportion of a paranitroso dialkyl aniline in an amount sufiicient to inhibit the deleterious effects of oxidation.

2. A viscous mineral oil fraction of the lubricant type selected from the group consisting of highly refined oils and solvent-refined oils and having in admixture therewith a minor proportion of a paranitroso dimethyl aniline in" an amount suflicient to inhibit the deleterious effects of oxidation.

3. A viscous mineral oil fraction of the lubricant type selected from the group consisting of highly refined oils and solvent-refined oils having in admixture therewith a minor proportion of. a paranitroso diethyl aniline in an amount sumcient to inhibit the deleterious effects of oxidation.

4. An improved mineral oil composition comprising a viscous mineral oil fraction of the lubricant type selected from the group consistingof highly refined oils and solvent-refined oils having in admixture therewith a. minor proportion of a' paranitroso dialkyl aniline in sufilcient EVERETT W. FULIER. 

